1. Field of the Invention
The present invention relates to a digital broadcasting system.
2. Description of the Related Art
Digital broadcasting has been developed in recent years so that a wide variety of programs can be provided on a large number of channels. For satellite digital broadcasting, large numbers of channels are possible by multiplexing the channels together into a single frequency band. This multiplexing is performed using what is called a “transport stream” under MPEG2 (Moving Pictures Experts Group2) standard. This technique is described in detail in the documentation for ISO/IEC Standard 13818-1 (MPEG2 system).
These satellite digital broadcasts consist of the one-way transmission of image information and other data from a transmitter station, so that no interaction with the receiver is possible. However, a greater variety of services would be possible if it were possible to enable the user of a receiver terminal to perform interactive operations for the image information.
As a result, various interactive systems have developed which use a telephone line or the like to connect the receiver terminal to the transmitter station. However, these systems require the provision of a separate communication line between each receiver terminal and the transmitter station, incurring significant connection charges.